Bipolar junction transistors (BJTs) may have desirable features from the viewpoint of current performance, speed, and gain compared to MOS transistors (MOS TRs: Metal Oxide Semiconductor Transistors) and are often used in analog, power, and RFIC applications. Bipolar transistors having an emitter, a base, and a collector may be classified into vertical bipolar transistors or horizontal bipolar transistors, depending the travel direction of electric charges emitted from the emitter.
In general, a PN junction where a P-type semiconductor region and an N-type semiconductor region are in contact with each other in a semiconductor substrate exhibits a rectification characteristic, which is a basic constituent component of a semiconductor device. A bipolar junction transistor (BJT, hereinafter, referred to as a bipolar transistor) may have two layers of PN junctions. A forward bias may be applied to one PN junction of the bipolar transistor and a reverse bias may be applied to the other PN junction to induce movement of electrons and holes. In manufacturing an NPN bipolar transistor, an interval may be provided between an emitter and an extrinsic base to obtain a desired breakdown voltage.
A bipolar transistor in accordance with related art is illustrated in FIG. 1. FIG. 1 is a sectional view showing the structure of a bipolar transistor. In a semiconductor device having a bipolar transistor structure shown in FIG. 1, N-type sub collector 20 may be formed on the surface of P-type silicon substrate 10.
Epitaxial layer 30 may be formed on semiconductor substrate 10 including N-type sub collector 20. A device isolation film (not shown) may define an active region in epitaxial layer 30 and may be formed into epitaxial layer 30. Intrinsic base region 40 may be formed in the active region inside the device isolation film through P-type impurity ion implantation. Emitter region 50 may be formed in intrinsic base region 40 and extrinsic base region 52 may be formed in both sides of emitter region 50. Collector region 60 and emitter region 50 may be formed through N-type impurity ion implantation and the extrinsic base region 52 may be formed through P-type impurity ion implantation.
In the bipolar transistor of the related art having the above-described structure, the base-collector junction may be formed through ion implantation and diffusion. During the formation of the base-collector junction, the areas (a) and (b) of intrinsic base region 40 and collector region 60 may increase, resulting in the distance (c) between extrinsic base region 40 and collector region 60 increasing, which in turn causes an increase in the total transistor area.
In the bipolar transistor of the related art, since the base, the emitter, and the collector may be formed through an ion implantation process, photo masks are inevitably used for this process. Due to the necessity of using photo masks, the process complexity is relatively high, thus have negative effects on yield, performance, and manufacturing costs.